Ring-opening polymerization of DL-lactide (LA) has been initiated with the (eta(3)-C3H5)(2)Sm(mu(2)-Cl)(2)(mu(3)-Cl)(2)Mg(tmed)(eta(2)-Cl)Mg(tmed) complex both in bulk and solution. The effects of reaction conditions, such as reaction time, reaction temperature, and monomer/initiator molar ratio on the polymerization has been discussed. The results showed that (eta(3)-C3H5)(2)Sm(mu(2)-Cl)(2)(mu(3)-Cl)(2)Mg(tmed)(mu(2)-Cl)Mg(tmed) was more effective for the polymerization of LA, and high molecular weight of polylactide was obtained by this initiator. The solvent affected the polymerization significantly. The polymerization mechanism was in agreement with the coordination mechanism. The polymer was characterized by FTIR, H-1-NMR, and DSC.